In recent years, power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air cells have been developed.
An active material is formed over a surface of a current collector, so that an electrode for a power storage device is formed. As the active material, a material which can store and release ions functioning as carriers, such as carbon or silicon, is used. For example, silicon or phosphorus-doped silicon, which has larger theoretical capacity than carbon, excels at increasing of the capacity of a power storage device. However, silicon generates stress due to volume expansion when charged, which causes the active material to be separated from the current collector, for example, so that the charge-discharge cycle characteristics of the power storage device are deteriorated. Thus, some techniques for suppressing the effect of the volume expansion of the active material have been proposed (for example, Patent Document 1).